1. Field of the Invention
The present invention relates to a control system having a plurality of control devices that are connected to a network, and control objects to be controlled different from each other.
2. Background Art
Up to now, as a control system high in reliability, a control device illustrated in FIG. 14 is known. Referring to FIG. 14, the control device includes a main CPU (central processing unit) 51, and a sub CPU 52. The sub CPU 52 has a D.P. RAM (dual port RAM), and communicates data with the main CPU 51 through a communication line 53. The control device also includes an output stop circuit 54 that stops an output in a defective state.
In the related-art control system, in order to improve the reliability of computation, two CPUs are used in the control device as described above, and the control is executed by so-called CPU multiplexing. In this control device, the same data is input to the respective CPUs, the input results are compared by the D.P.RAM of the CPU 52, and the input results are compared with the main CPU 51 and the sub CPU 52. A defect is detected by a difference in the comparison result. When the defect is detected, the output stop circuit 54 stops the output to improve the reliability of operation (for example, refer to Patent Document 1 (JP-A-H03-286340)).
Also, up to now, a control system has been proposed which enhances the reliability as illustrated in FIG. 15. The control system in FIG. 15 includes an A-system control device 1, a B-system control device 2, and a C-system control device 3 each of which is a single control device. The A-system control device 1, the B-system control device 2, and the C-system control device 3 are coupled to each other through a signal line 5, and communicate data with each other through the signal line 5. An object to be controlled 4 is controlled by the A-system control device 1, the B-system control device 2, and the C-system control device 3.
A synchronous interrupt control is conducted among the A-system control device 1, the B-system control device 2, and the C-system control device 3 according to an interrupt control signal from an interrupt control line 6. Also, the respective computer control devices of the A-system control device 1, the B-system control device 2, and the C-system control device 3 are coupled to the object to be controlled 4 through a control I/O line 7. A system configuration control line 8 selects a device that conducts a control output from one of the computer control devices in the A-system control device 1, the B-system control device 2, and the C-system control device 3, and conducts control.
The A-system control device 1 includes an computation device 10 that conducts the main computation of the computer control device, a diagnosis device 11 that detects an computation state of the computation device 10, an output device 12 that outputs computation output data of the computation device 10, an input device 13 that inputs the computation input data to the computation device 10, an computation output switch device 14, a synchronous interrupt control device 15 that conducts the synchronous interrupt control of the computation device 10, and a communication device 16 that exchanges control data with respect to other control devices.
Likewise, the B-system control device 2 includes an computation device 20, a diagnosis device 21, an output device 22, an input device 23, an computation output switch device 24, a synchronous interrupt control device 25, and a communication device 16. The C-system control device 3 includes an computation device 30, a diagnosis device 31, an output device 32, an input device 33, an computation output switch device 34, a synchronous interrupt control device 35, and a communication device 36.
In the related-art control system configured as described above, the control devices 1, 2, and 3 are synchronized with each other through the interrupt control line 6, exchange control input data input from the control I/O line 7 with each other through the communication line 5, and after confirming that the input data is the same, implement the same computation. Then, the control outputs from the respective control devices as the operation results are subjected to majority decision to detect the defect of the computation results. When the defect is detected by the majority decision, the output is stopped by the computation output switch device of the control device to improve the reliability of the computation (for example, refer to Patent Document 2 (J2-A-H04-307633)).